Add fix delay after send/request to allow RS485 adapter to switch in modbus (#51417)

homeassistant/components/modbus/modbus.py

@@ -329,6 +329,10 @@ class ModbusHub:
         if not self._client.is_socket_open():
             return None
         async with self._lock:
-            return await self.hass.async_add_executor_job(
+            result = await self.hass.async_add_executor_job(
                 self._pymodbus_call, unit, address, value, use_call
             )
+            if self._config_type == "serial":
+                # small delay until next request/response
+                await asyncio.sleep(30 / 1000)
+            return result

tests/components/modbus/test_init.py

@@ -325,9 +325,13 @@ SERVICE = "service"
     [
         {
             CONF_NAME: TEST_MODBUS_NAME,
-            CONF_TYPE: "tcp",
-            CONF_HOST: TEST_HOST,
-            CONF_PORT: 5501,
+            CONF_TYPE: "serial",
+            CONF_BAUDRATE: 9600,
+            CONF_BYTESIZE: 8,
+            CONF_METHOD: "rtu",
+            CONF_PORT: "usb01",
+            CONF_PARITY: "E",
+            CONF_STOPBITS: 1,
         },
     ],
 )